Re: Speeding up chunk size change?

[Steven Haigh <netwiz@crc.id.au>]

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On 4/03/2012 1:24 PM, Stan Hoeppner wrote:
> On 3/3/2012 6:56 PM, Steven Haigh wrote:
>> On 4/03/2012 8:42 AM, Stan Hoeppner wrote:
> [snip]
>>>> blockdev --setra 8192 /dev/sd[abcdefg]
>>>
>>> Read-ahead is per file descriptor, and occurs at the filesystem level.
>>> The read-ahead value used is that of the device immediately underlying
>>> the filessytem.  So don't bother setting these above.
>>
>> Interesting - I didn't think that was the case for whole disk arrays -
>> but there you go... Learnt something else :)
> [snip]
>>>>           echo 4096>   /sys/block/$i/queue/read_ahead_kb
>>> Eliminate this line ^^^^
>>
>> Any insight into why? I would have thought that this would help -
>> however I'm not quite sure as to the values - as this is much less than
>> one chunk... That also being said, wouldn't it be a good idea to have
>> *some* readahead?
>
> You read the answer up above, and commented on it.  Maybe you didn't
> fully understand?  Or maybe it's because you don't know that these two
> are functionally equivalent?
>
> blockdev --setra X
> echo X>   /sys/block/$i/queue/read_ahead_kb

Ahhh - you're spot on... I didn't think they had the same functionality!

-- 
Steven Haigh

Email: netwiz@crc.id.au
Web: http://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897
Fax: (03) 8338 0299


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